Most tractor manufacturers do not test differential and its lock during assembly and those testing these parts generally perform field tests. It should be mentioned that field tests are dangerous and, since these parts are quite sensitive, it is impossible to identify all of their shortcomings. There is no device performing such assessments. Therefore, given the important function of tractor differential, it proves essential and crucial to have a device testing these parts during assembly. Bearing this necessity in mind, the first step in designing a test device for differential and its lock which works with every kind of tractors was taken.